Initial

The construction of the Palm Islands and The World
was immediately felt by the surrounding ecosystem. Sand dredging and
depositing resulted in the burial, death, and asphyxiation of a variety
of wildlife. In addition, the project has resulted in increased fine
sediment suspension in the waters off the coast of Dubai. Such sediment
suspension allows less light to filter to the sea floor, and can
suffocate and endanger the health of marine life in the area.

Dredging and Beach Nourishment/Development

Beach nourishment/development refers to the process used to either add to an existing beach, or, as is the case with the Palm Islands, to build an entirely new beach. Dredging is the process by which sand is collected, or dredged, from one location, usually the intertidal zone, and deposited on the existing beach. Beach nourishment is especially common along the U.S. Atlantic coast, where areas such as the Outer Banks in North Carolina have valuable stakes in the condition of their coastlines. With much development and tourism concentrated in such areas which are particularly vulnerable to coastal erosion and storm-based changes, beach nourishment represents an important and strategic means of "protecting" coastal economic interests.

The Dredging Process:

Sand for the Palm Islands was dredged form the sea floor in the Persian Gulf near the islands, and transported via a "rainbowing" process (shooting the sediment in an arch to the islands' location) to build the actual island. Hopper and cutter dredges were used for the dredging process. Cutter dredges draw sediment (sand, gravel, etc.) from the seafloor via a rotating cutter and centrifugal pump which turn the sediment mixture into slurry. A network of floating and submerged pipes then transports the water to the nourishment site. Cutters work well in situations when the sediment being extracted is particularly compact. (Greene 2002) Hopper dredges suctions layers from the seafloor using a hydraulic pump, then transports the material to the site through a pipe system. Water is drained out of the original sediment, so the slurry produced by a cutter dredge is avoided. Various machinery, namely bulldozers, are then used to shape the beach and disperse the imported sediment. (Greene 2002)

One
of the primary initial effects of nourishment, both at the mine and nourishment sits, and along the piping in between, is the suspension of fine silt and clay sediments in the surrounding
waters. Since fine sediments stirred up by the dredging process take longer to
settle, they remain suspended in the water for longer periods of time. Nakheel also failed to use silt screens while dredging in order to keep turbidity low at the dredge sites (Salahuddin 2006). These
finer sediments often result in the asphyxiation of fish and benthic fauna,
such as crustaceans and echinoderms, as they become lodged in gills and lungs
of organisms while they are breathing. Studies in the U.S. have shown that sediment from turbid environments have also inhibited filter feeders such as clams and crabs by decreasing their food intake by 30-40.5%. Many species are also simply suffocated
by the mere shifting of sediment during the mining process, or are killed from being sucked into the hoppers themselves. As benthic
organisms serve as a major food source for a variety of marine animals, a
decrease in their population also has adverse effects on all upper levels of their
food chain. In addition, an increased level of particles in the water can "reducegrowth and increase calcification rates in coral reefs" (Greene 2002), threatening those reefs that may have survived the initial development. A study in Miami showed that fourteen years after a nourishment event, coral heads were sill dying. (Greene 2002)

Suspended sediments in both sites can also prevent sufficient
sunlight from reaching the lower depths of water; as species die off,
decomposed organic materials can increase hydrogen sulfide levels in the water,
making it toxic. It is often impossible for an ecosystem to revive after such
an event, and in the rare cases where recovery has occurred, the time needed
was over a year. In past U.S. dredging situations where such toxification did
not occur, and when conditions were more favorable towards species re-growth,
it has typically taken around a year for the ecosystem of the mine site to
re-equilibrate itself. In general, biomass takes at least 1.5 years and up to
2.5 years to recover itself. Other effects from suspended sediment include decreased visibility, making it more difficult for organisms to locate prey, as well as changes in the chemistry of the water affected. As disturbed particles settle on the ocean floor, they can inhibit the functioning of bottom feeders, kill micro-plants, and inhibit the spawning and hatching of various types of fish. It is also very common for fine sediments to become re-suspended multiple times during the years following development as they settle on the very top layer of the seabed.

The settling of suspended sediment is dependent on four main factors:

"1) wave
energy (more
turbid during storms)

2) amount of sand placed on the beach (more sand may
increase turbidity)

3) the quality of the sand (higher content of silt/clay caused elevated
levels)

4)the
mode of placement (i.e., hydraulic pipeline or barge pump-out)"

(Greene 2002)

Benthic recovery in dredged areas in the U.S. has been found to be dependent on
a number of factors including "1) duration and
timing of dredging; 2) the type of dredging equipment used to extract the
sediment; 3) sediment composition of the mine site; 4) amount of sand removed
from the site; 5) the fauna present in the mine pit and surrounding area prior
to dredging and their ability to adapt to change; 6) characteristics of the new
sediment interface; 7) life history characteristics of fauna that recolonize;
8) water quality at the site; 9) hydrodynamics of the mine pit and surrounding
area; and 10) degree of sedimentation that occurs following dredging [. . .] In
general, it appears that areas where biological impacts are greatest and most
prolonged, are areas where bottom sediment composition has been altered"
(Greene 2002)

The effects of dredging on fish are more varied. It is often difficult to measure effects of such development on fish species since they are always in motion, and because initial turbidity can decrease on a timescale from hours to days (though there have been cases studied in which turbidity remained and inhibited visibility up to seven years following initial development - Greene 2002). In some instances, however, the nutrients churned up by the mining process have shown to increase the abundance of various species of fish; in others, while fish have left during the initial period of disturbance, they have eventually returned; in yet third instances, native fish species have left the area while new species moved in. Various sources cite the difficulty of measuring the impact on fish given the tendency of fish to naturally move from place to place. In fact, the greatest effects to fish species can be found in those that prey on benthic organisms, which are most sensitive to the initial mining process.

The effects on marine mammals are more direct, and often result either from the disruption of feeding grounds, or direct collisions with the boats or dredging equipment, as has been the case with sea turtles in the United States. Lighting used by the boats can also confuse sea turtle hatchlings, or throw off other marine mammals and predatory fish, especially at night. Still, some species, such as Pacific Salmon, can benefit from increased turbidity, as they become less visible to predators.

Local diving associations in the area near Palm Jumeirah also reported that a slimy grey cement-like substance had been found on the beaches near Palm Jumeirah following the construction of the island. Sources later confirmed that the sediment was caused by the deep-sea mining of sediment for the islands. (Salahuddin 2006)

Microclimate Effects of Buildings in Dubai

So far effects on the macroclimate have
been addressed, but what about the effects on the localized climate conditions within an urban area - its microclimate?

Background of Dubai's Climate:

Dubai is located on the southern end of the Gulf. Its climactic cycle
can be divided into three periods, (December to March) which has mild weather
and temperatures of 20-23 C, (November to April) which has warm weather and
temperatures of 25-26 C and (May to October) which has hot weather and
temperatures of 29 to 34 C. The first two periods are relatively comfortable if
it is well-shaded and there are continuous breezes from the Gulf. The hot
period is more burdensome because of the high incidence of solar radiation,
humidity, and limited evaporative cooling. Yet, there is relief from nocturnal
radiative cooling which happens year-round and winds traveling at velocities
4.0m/s (Thapar & Yannas, 2007).

Microclimate Effects of Buildings:

There are three types of structures being built in Dubai: high
skyscrapers, mid-rise blocks, and low-rise compact courtyard structures. Each
has different shading effects on the ground. Below is a diagram illustrating
exactly those effects of the different types of structures with the same
volumes. Courtyard structures and more dense developments provide better
shading for streets and people. However, future plans are gearing toward the development of high-rise buildings because of advantages such as privacy, exclusivity and views.

Top Left Corner: High-rise building

Top Right Corner: Mid-rise building

Low-rise, Courtyard Building

There was a study done on the effects of different built forms on ambient
temperature and airflow. The results revealed that during the daytime, the
low-rise courtyard form left a larger microclimatic footprint because more of
its mass was constructed closer to the ground. In terms of temperature, the
courtyard was coolest out of all the structures and the open courtyard being
the absolute coolest. However, because of the obstruction of airflow in
courtyard forms, courtyards had the lowest wind speeds, and as a result, were
warmer in the areas where there was less wind movement (east-west as opposed to
north-south) (Thapar & Yannas, 2007).

Envi-met predictions of air temperatures for 2:00pm on a July day around a constant built volume on a 100x100m site. First picture on the left represents a high-rise building, second, mid-rise, and last, courtyard blocks.

The conclusions to this study include that built forms of any kind
should strive to incorporate well-shaded and ventilated spaces. Water can help
provide cooling, although humidity is still a challenge. Vegetation can also
help with cooling and increase the market value of property, but humidity and
the high-cost of maintenance may pose challenges. Shading, permeability to
airflow for convective cooling and the employment of right construction
materials are indispensable for sustainable urban designing. (Thapar & Yannas, 2007)